In a wireless communication system, a variety of errors are inherent to radio frequency (RF) signal propagation over the air interface, thus making data transmission difficult. Because a radio frequency (RF) channel experiences multi-path fading, path loss that becomes serious as a mobile station (MS) is further from a Base Station (BS), etc. as well as thermal noise modeled as Additive White Gaussian Noise (AWGN), it is more difficult to transmit a signal reliably.
To ensure transmission reliability against various changes in channel status and errors during wireless communications, techniques such as 1) Forward Error Correction (FEC) or channel coding, and 2) Automatic Repeat reQuest (ARQ) or Hybrid Automatic Repeat reQuest (HARQ) are widely used.
Among them, HARQ will be described in brief.
FIG. 1 illustrates a signal flow referred to for describing the principle of HARQ.
Referring to FIG. 1, HARQ is a hybrid technology of conventional schemes in combination, that is, ARQ in the Medium Access Control (MAC) layer and channel coding in the physical layer. In HARQ, an erroneous initial transmission packet P1A is stored until a retransmission signal P1B is received because the initial transmission packet P1A retains information to a certain extent despite errors, and decoded after being soft-combined with the retransmission signal P1B or along with the retransmission signal P1B without soft combining.
The initial transmission signal P1A and the retransmission signal P1B are the same or different transmission packets created from the same channel encoder input packet P1. A packet P2A is produced from a new channel encoder input packet P2.
Although data has been transmitted according to the scheduling standard, the data may be unexpectedly lost or damaged during the transmission process. In this case, there are proposed a variety method for controlling the faulty or erroneous operation, for example, an automatic repeat request (ARQ) scheme and a HARQ scheme, etc. The ARQ scheme waits for transmission of the acknowledgement (ACK) signal after transmitting a single frame. If a receiver correctly receives data of the frame, it transmits the ACK signal. However, if an unexpected error occurs in the frame, the receiver transmits a negative-ACK (NACK) signal, and deletes the received erroneous frame from its own buffer. If the transmitter receives the ACK signal, it transmits the next frame. Otherwise, if the transmitter receives the NACK signal, it retransmits the frame. Differently from the ARQ scheme, the HARQ scheme allows the receiver to transmit the NACK signal to the transmitter on the condition that the received frame cannot be demodulated. However, the HARQ scheme does not delete the pre-received frame from the buffer, and stores the same in the buffer for a predetermined period of time. Therefore, if the above-mentioned frame is retransmitted, the HARQ scheme combines the pre-received frame with a retransmitted frame, and increases the success rate of data reception.
In recent times, the HARQ scheme has been more widely used than the ARQ scheme. There are various kinds of HARQ schemes. Likewise, if the receiver has failed in decoding reception (Rx) data, it can transmit the HARQ feedback signal (ACK/NACK) to the base station.
However, information indicating which channel will be used for a specific mobile station to be used for transmission of a feedback signal (i.e., ACK/NACK) in association with one or more downlink bursts, and other information indicating a method for transmitting such a feedback signal on the condition that multiple codewords are applied to one downlink burst have not been investigated yet. In addition, under a wireless communication environment involving a plurality of mobile stations, information indicating a method for constructing HARQ feedback channel (HFBCH) transmitted from each mobile station and another information indicating whether to transmit the constructed HARQ feedback channel (HFBCH) to the base station have also not been investigated yet.